The present invention relates to a method for operating a direct-injecting gasoline internal combustion engine, especially of a motor vehicle. In the method, gasoline is directly injected into a combustion chamber of the engine and an ignition spark is ignited in the combustion chamber.
The invention furthermore relates to a storage element for a control apparatus of a direct-injecting gasoline internal combustion engine especially of a motor vehicle. A computer program is stored on the storage element and can be run on a computing apparatus, especially on a microprocessor. The storage element is, for example, configured as a read-only-memory, a random-access-memory or as a flash memory.
The present invention also relates to a computer program which can be run on a computing apparatus, especially on a microprocessor.
Finally, the invention relates to a control apparatus for a direct-injecting gasoline internal combustion engine, especially of a motor vehicle. The control apparatus serves for controlling the injection of gasoline into a combustion chamber of the internal combustion engine and the ignition of an ignition spark in the combustion chamber.
In direct-injecting gasoline internal combustion engines known from the state of the art, gasoline is injected directly into the combustion chamber of a cylinder of the internal combustion engine. The air/gasoline mixture, which is compressed in the combustion chamber, is then ignited by igniting an ignition spark in the combustion chamber. The volume of the ignited air/gasoline mixture expands explosion-like and imparts movement to a piston which is reciprocally movable in the cylinder. The reciprocal movement of the piston is transmitted to a crankshaft of the engine.
Direct-injecting internal combustion engines can be driven in various operating modes. As a first operating mode, a so-called stratified operation is known which is used especially for smaller loads. As a second operating mode, a so-called homogeneous operation is known which is utilized with larger loads applied to the engine. The various modes of operation are distinguished especially as to the injection time point and the injection duration as well as with respect to the ignition time point.
In stratified operation, the gasoline is injected into the combustion chamber during the compression phase of the engine in such a manner that a fuel cloud is disposed in the direct vicinity of a spark plug at the time point of ignition. This injection can take place in various ways. Accordingly, it is possible that the injected fuel cloud is already at the spark plug during or directly after the injection and is ignited by the spark plug. Likewise, it is possible that the injected fuel cloud is guided by a charge displacement to the spark plug and is only then ignited. In both combustion methods, no uniform fuel distribution is present in the combustion chamber, rather, a stratified charge is present.
The advantage of the stratified operation is that the applied smaller loads can be carried out by the engine with a very low fuel quantity. Larger loads can, however, not be satisfied by the stratified operation.
In the homogeneous operation, which is provided for such large loads, the gasoline is injected during the induction phase of the engine so that a swirling and therefore a distribution of the gasoline in the combustion chamber takes place easily already in advance of the ignition. Thus, the homogeneous operation corresponds approximately to the type of operation of internal combustion engines wherein fuel is injected into the intake manifold in a conventional manner. As required, the homogeneous operation can be used also for smaller loads.
In the stratified operation, a throttle flap is opened wide in an intake manifold leading to the combustion chamber and the combustion is controlled essentially (open loop and/or closed loop) only by the fuel to be injected. In homogeneous operation, the throttle flap is opened or closed in dependence upon the requested torque and the fuel mass, which is injected, is controlled (open loop and/or closed loop) in dependence upon the inducted air mass.
In both operating modes, that is in stratified operation and in homogeneous operation, the fuel mass, which is to be injected, is additionally controlled (open loop and/or closed loop) in dependence upon a plurality of additional operating variables to an optimal value with respect to a saving of fuel, exhaust-gas reduction, noise reduction and the like. The control (open loop and/or closed loop) is different in the two modes of operation.
In jet-guided BDE combustion methods in stratified operation, it is purposeful to ignite directly in front of an injection nozzle, that is, at the jet root. This can be reliably achieved in that the spark gap of a spark plug is arranged in the region of the jet root and the ignition spark burns at a time point at which the geometric jet end of the injected gasoline jet passes the spark gap. In the jet-guided BDE combustion method, injection is very late and the piston is already disposed close to top dead center. For this reason, the density of the air/fuel mixture, which is disposed in the combustion chamber, is very high. This has a high ignition voltage requirement and is typically approximately 25 kV at an electrode spacing of 1 mm. Electrode distances of significantly more than 1 mm cannot be realized with an ignition voltage of approximately 30 kV which is available at the present time.
The foregoing notwithstanding, it is especially the desire for the jet-guided BDE combustion method to be able to realize electrode distances of significantly more than 1 mm, for example, 5 mm or more in order, for example, to be able to ignite a plurality of individual jets of a multi-hole nozzle in common or to be able to ignite transversely through the jet root of the injection jet. Large electrode gaps of this kind would require, however, ignition voltages of significantly more than 50 kV to ignite the air/gasoline mixture. These ignition voltages are not realizable because of the size, the needed insulation complexity and the high costs.
The present invention is therefore based on the task of making possible the safe and reliable ignition of an air/gasoline mixture in a combustion chamber of a direct-injecting internal combustion engine at a relatively low ignition voltage with a spark plug having a clearly increased electrode gap.
To solve this task, the invention proceeds from the method of operating a direct-injecting gasoline internal combustion engine of the type mentioned initially herein by suggesting that the ignition spark is ignited in advance of the injection and a spark duration beyond the end of the injection is maintained.
According to the invention, the ignition spark is ignited at such an early time point that the ignition voltage, which is applied to the spark plug, is sufficient notwithstanding a large electrode gap because of the then relatively low density in the combustion chamber. At the time point of the ignition of the ignition spark, the piston is disposed still relatively far from top dead center and the volume, which is contained in the combustion chamber, is not yet especially intensely compressed. The ignition spark will then burn up to beyond the end of the subsequent following injection. The combustion voltage of a spark plug is considerably less than the ignition voltage. For this reason, the conventional voltage of approximately 30 kV, which is applied to the spark plug, is sufficient notwithstanding the clearly increased electrode gap in order to reinforce the spark and to thereafter permit combustion with increasing density.
According to the invention, it has been recognized that especially for a jet-guided combustion method in stratified operation, the actual time interval, which is required for a successful ignition of the air/fuel mixture, is coupled closely to the end of the injection because the mixture can only successfully thoroughly combust when the jet end is ignited. This means that it is only important to cover this actual time interval of the combustion duration of the ignition spark. It is, however, of no significance when the ignition spark is ignited clearly earlier or burns clearly later. The thermodynamically relevant time-dependent position of the centroid of the combustion therefore is especially dependent upon the start and the duration of the injection.
The temperature, which is required for the combustion of the air/fuel mixture, is not brought forth within the shortest time by an ignition spark which is applied for a short time. Rather, the required ignition energy accumulates over a longer time span, namely, from the ignition of the ignition spark in advance of the start of the injection up to reaching the actual time interval subsequent to the end of the injection.
According to an advantageous further embodiment of the invention, it is suggested that the internal combustion engine is driven in a stratified operation. Furthermore, it is suggested that the internal combustion engine is operated jet-guided. Additional information as to the jet-guided BDE combustion method can be obtained from the text xe2x80x9cKraftfahrtechnisches Taschenbuch/Boschxe2x80x9d, 22nd edition, Springer-Verlag, 1998, page 369. Reference is expressly made to this publication.
According to another advantageous embodiment of the present invention, it is suggested that the spark duration is maintained until the geometric end of an injection jet has passed the ignition location. According to this embodiment, the fact is taken into account that the air/fuel mixture can only successfully thoroughly combust when the jet end is ignited. By means of an ion flow probe projecting into the combustion chamber, it can, for example, be determined when the jet end has passed the ignition location. Further information as to the ion flow measuring method is provided in the xe2x80x9cKraftfahrtechnisches Taschenbuch/Boschxe2x80x9d, page 442. Reference is expressly made to this publication.
Of special significance is the realization of the method of the invention in the form of a storage element which is provided for a control apparatus of a direct-injecting gasoline internal combustion engine, especially of a motor vehicle. A computer program is stored on the storage element which can be run on a computing apparatus and especially on a microprocessor and is suitable for carrying out the method of the invention. In this case, the invention is therefore realized by a computer program stored on the storage element so that this storage element, provided with the computer program, defines the invention in the same way as the method for whose execution the computer program is suitable. As a storage element, an electric storage medium can be used, for example, a read-only-memory, a random-access-memory or a flash memory.
The invention also relates to a computer program of the kind mentioned initially herein which is suitable for carrying out the method of the invention when it runs on the computing apparatus. It is especially preferred when the computer program is stored on a storage element especially on a flash memory.
As an additional solution of the task of the present invention, and proceeding from the control apparatus for a direct-injecting gasoline internal combustion engine of the type mentioned initially herein, it is suggested that the control apparatus triggers an ignition of the ignition spark in advance of the injection and initiates a spark duration up to beyond the end of the injection.
Finally, as a further solution of the task of the present invention and proceeding from the direct-injecting gasoline internal combustion engine of the type mentioned initially herein, it is suggested that the ignition equipment ignites the ignition spark in advance of the start of the injection and supplies a spark duration up to beyond the end of the injection.